This invention relates to new and useful improvements to a tubular pole piece assembly for stringed musical instrument pickups such as pickups for guitars and the like although it is not restricted to use with guitars. As is conventional in the prior art, the tubular pole pieces are contained within the inner core of a wire-wound field of the pickup and each string is served by a separate, solid, tubular pole piece positioned directly under, and in the center of the vibrational loop path of the string.
Each tubular pole piece is energized by means of direct contact with a permanent magnet bar of ceramic, Alnico, or other preferred permanent magnet material. As is functionally applied in prior art, the tubular pole piece emits magnetic flux, or force upwardly into the vibrational loop of the string to magnetize the string. When plucked, the motion of the string cuts the flux lines disturbing the magnetic field of the tubular pole piece to create inductive force into the resistive field coil, converting mechanical motion into electrical current, or signal for amplification.
The disadvantage of prior art pole piece types, specifically, solid steel rod (e.g. U.S. Pat. No. 3,983,778) solid steel machine screw (e.g. U.S. Pat. Nos. 2,175,325 and 3,715,446) and solid Alnico rod permanent magnets (e.g. U.S. Pat. No. 4,320,861) is their concentration of diametric central magnetic force against the vibration, or free movement of the string. The prior art pole piece end face emits motion restricting magnet force centrally and longitudinal with the string. As will be described the zone of strongest magnetic force is in the direct center of the pole piece end face under and along the vibrational loop path of the string.
The motion limiting effect of the magnetic force field multiplies progressively as string lengths are physically shortened by depressing the strings onto the frets, particularly in upper registers of the fingerboard of the instrument where the highest frequencies originate. The vibration loop of the string decreases in width as frequencies increase in Hertz, or cycles per second. Narrower high frequency vibration loops have less momentive inertia to vibrate freely and to full potential within the strong magnetic force field.
Fundamental note definition, intricate harmonic overtones, precise note intonation within chord forms, sustain time, and a degree of output signal, or power value to the amplifier, are sacrificed because the string is physically unable to vibrate freely enough to develop a perfect harmonic spectrum.